The present invention relates to a fuel injection control system for an internal combustion engine.
Conventionally, there has been proposed a system for controlling fuel injection and spark ignition from the first revolution of the internal combustion engine by detecting a crank angle position before starting up the engine (on state of a key switch) (Japanese Unexamined Patent Publication No. 60-240875).
Employing the above-mentioned system, it becomes possible to perform independent synchronous injection from starting-up of the internal combustion engine. A timing chart excluding fuel injection portions (first injection signals for #1 and #3 cylinders) under asynchronous injection in FIG. 2 corresponds the operational timing of the above-mentioned system. It should be noted that n-th cylinder will be expressed as #n cylinder throughout this specification. Fuel injection in this system is normally initiated at a fuel injection initiation timing at approximately 90.degree. CA (crank angle) before opening of an intake valve. Accordingly, the cylinder, for which an injection pulse is first transmitted, is #4 cylinder in FIG. 2. Namely, despite the fact that the intake valve of #3 cylinder is open, fuel injection does not take place for the #3 cylinder. This causes a delay in the extend of 180.degree. CA to first combustion in case of a 4-cylinder internal combustion engine. As a solution for this, a system performing asynchronous injection for #1 and #3 cylinders has been proposed (Japanese Unexamined Patent Publication No. 60-111042). This may eliminate a delay to the first combustion and permits the internal combustion engine to start-up more quickly.
In the above-mentioned system, asynchronous injection of fuel takes place irrespective of crank angle positions of respective cylinders. Therefore, as in the #1 cylinder of FIG. 2, injected fuel can be divided to the next cycle (720.degree. CA later). Then, division of the injected fuel is caused, misfiring due to lean mixture for lack of fuel can be caused to exhaust non-combustioned HC.